1. The Field of the Invention
The present invention relates generally to dental instruments. More particularly, the present invention relates to an endodontic instrument for use in an endodontic procedure that has an adjustable working length.
2. The Relevant Technology
In order to preserve a tooth that has diseased pulp material therein, it is necessary to prevent bacterial proliferation within the pulp canal of the tooth by removing the diseased or necrotic pulp material from the pulp cavity or root canal. After the pulp material has been removed or extirpated from a tooth, the pulp cavity or root canal is typically filled or obturated with an inert material before being sealed off with an inert sealer of an aseptic material in order to prevent future infection of the tooth root. This procedure is referred to as root canal therapy.
During root canal therapy, it is essential that the entire root canal, including the root tip, be cleaned and filled to eliminate all organic matter contained within the root canal. The typical method followed for root canal therapy is to open the tooth to the pulp chamber and then work down to the root end. Root canal cleaning or preparation is generally achieved by hand or mechanical instrumentation with files or bits that are configured to bore and/or cut. In order to gain access to the pulp chamber in a tooth, a hole is drilled through the tooth to the pulp chamber and subsequently widened. A variety of endodontic instruments are then used to enlarge and clean out the root canal to remove all the pulp tissue.
Conventional dental instruments used during root canal therapy such as various file instruments generally include a thin, flexible, metal shaft or file with an abrasive surface or sharp edges, which enables efficient cleaning of the root canal. A handle or hub end is securely affixed at one end of the file instrument and is adapted for gripping by an operator or attachment to a mechanical device such as a dental drill.
It is often necessary to repeatedly insert and remove various file instruments into the root canal of a tooth during root canal therapy. Extreme care must be taken to prevent penetration of such file instruments beyond the root canal apex in order to avoid injury and possible infection of the adjacent periodontal tissue and bone structure. The file must be inserted no more than a specific maximum distance inside the root of the tooth. The occurrence of errors in depth penetration of the file into the root canal, either too deep or too shallow, are the major cause of failure in endodontic procedures. Thus, it is important in the preparation of the root canal to control the working length of the file utilized. Since it is physically impossible for a practitioner to see inside the tooth to the root apex, a determination must be made as to how far the file can enter the root.
Before a file instrument is inserted to remove the pulp material, the length of the root canal is determined to identify a suitable working length for the file instrument. Generally, the working length is the distance from a fixed reference position on the crown of a tooth to or near the apical constriction opening of the root canal. Typically, a practitioner initially ascertains the depth through which the various sized root canal instruments should penetrate into the root canal by utilizing an x-ray of the tooth. A full scale x-ray of the tooth is taken and the insertion distance is measured on the developed x-ray photograph by measuring the length of the tooth involved, as well as the length of the root canal therein.
A significant problem that can result from root canal cleaning is apical perforation from insertion of a file or shaft of a file instrument to the apex of the root canal. Perforating the apex can result from an error in estimating or measuring the length of a root canal. Similarly, the apex can be perforated by extrusion of infected pulp material through the apex due to the force exerted by the file on the pulp material as the file is pushed downward to reach the apex. In addition to exposing the tissue surrounding the tooth to the infected pulp material, apical perforations also substantially complicate subsequent filling of the root canal with a filling or obturating material.
Various techniques and devices have been developed for limiting the depth of penetration of dental instruments to the root canal tip. For example, once the length of the root canal has been determined, it is possible to use a dental instrument having a file extending beyond the handle by the predetermined maximum allowable length.
More commonly, an adjustable stopper has been typically placed over each dental instrument along the shaft or file so that the distance between the tip of the instrument and the stopper equals the distance between the top or the occlusal surface of the tooth and the apex of the root canal. Thus, the stopper sets the root canal instrument to the proper length or penetration depth for the root canal. The stopper located at the proper point along each root canal instrument intended to be used ensures that the instrument is inserted the proper depth into the root canal.
Examples of instruments utilizing stoppers are shown in FIG. 1 and FIG. 2 respectively at 10 and 20. Instrument 10 has a peanut-shaped handle 12 which is particularly adapted to be gripped by a practitioner during a root canal procedure. Handle 12 is accordingly typically used for manual filing. Instrument 20 has a latch handle 22 for attachment to an endodontic handpiece for rapid rotation as shown in FIG. 3 at 60. A stopper 40 is shown positioned on file 14 of instrument 10 and on file 24 of instrument 20. Such stoppers are typically formed of a simple block of rubber or plastic material, or constructed of a housing and a compression spring. In addition to a single stopper as shown in FIG. 1 and FIG. 2, several movable stoppers may be utilized and positioned on the shaft such that one stopper abuts the handle. An additional example of an endodontic device utilizing stoppers is disclosed in U.S. Pat. No. 5,154,611 to Chen.
The position of the stopper on the file determines the working length of the instrument, which is the length of the file to be inserted into the tooth during treatment. As shown in FIG. 4, stopper 40 prevents further penetration of file 24 into the root canal of the tooth when the bottom surface of stopper 40 abuts the occlusal surface of the tooth 90 being treated, such as the incisal edge or cusp tip. In this manner, when the dental instrument enters the root canal, the dentist can limit insertion by observing the contact of the stopper at the edge of the tooth.
Since a variety of file instruments are used throughout the root canal procedure, conventional practice has been to individually measure and position the stoppers on the various implements used. It is frequently necessary for the dentist to fit a stopper on the dental instrument while the patient's mouth is held open. Thus, it is desirable that the operation be carried out as fast as possible. At the same time it is essential that stoppers be placed with perfect accuracy, as otherwise the possibility of poking the instrument beyond the tooth is presented.
The problems with the conventional stopper procedure are numerous. The individual measurement and placement of the stoppers on the dental instruments is very time1 consuming and at times somewhat inaccurate. Each individual instrument and its stopper must be separately gauged against a separate scale or ruler and then individually set to the length indicated in an x-ray photograph. This procedure can involve inherent inaccuracies and a great deal of time and inconvenience to the dentist. In addition, there is also the potential for introduction of contaminants on the instrument during placement of a stopper thereon.
Further, the stoppers can be easily displaced or can slip from their intended position on the file instrument during use within the limited area of a patient's mouth and considering the relatively small size of the instruments involved. This can result in perforation of the apex of a tooth from failure of a stopper to remain at a predetermined position. It can also be difficult for the endodontist to precisely judge when the stopper has reached the surface of the tooth. Additionally, rubber stoppers may also be both flexible and movable and can therefore allow the file to proceed deeper into the root canal than may be desired.
Other devices have also been developed to limit the penetration of dental instruments into a root canal. For example, screw threads have been placed on the shaft of a file, with a nut threaded onto the file to act as a stopper. The manipulation of the file within a patient's mouth, however, can easily result in the nut being moved on the shaft.
In U.S. Pat. No. 4,028,810 to Vice, a root canal file is disclosed that includes a handle portion adjustably mounted in telescoping relation to the shaft of an elongated tool, with cooperating grooves in the shaft and handle preventing relative movement therebetween during use. The grooves around the shaft cooperate with mating ridges or grooves within the jaws of a tightening chuck on the handle to firmly interlock the handle and the shaft in any desired adjustment position.
Another endodontic instrument, disclosed in U.S. Pat. No. 4,165,562 to Sarfatti, includes a threaded base with a locking structure thereon and an elongated file projecting outwardly from the base. A threaded sleeve which acts as a stopper receives the base to facilitate longitudinal adjustment of the file relative to the sleeve. A plastic cap fits over the combination of the file and the sleeve and is imprinted with a plurality of graduations thereon to indicate the distance that the bottom of the file extends from the bottom of the sleeve.
While the above devices can limit the penetration of dental instruments into a root canal they are not adequately simple to use and manufacture. More importantly, however, conventional dental instruments do not provide a secure stopping capability while simultaneously enabling an instrument to be used with varying working lengths. Accordingly, there is a need for an improved endodontic device that overcomes or avoids the above problems.